Printed circuit board design support apparatus, method, and program medium therefor

ABSTRACT

Printed circuit board (PCB) design support apparatus and method are provided. The target element disposed on a front surface of the printed circuit board is mirror-copied, and then the straight line distance between the mirror copied element and a back element disposed on the back surface of the PCB is calculated under the condition that the thickness of the PCB is zero. The resultant creepage distance between the target element and the back element is obtained by adding the thickness of the PCB to the straight line distance. The creepage distance can be obtained accurately and quickly by a calculation on a straight line distance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for computer aided design, the systemtherefore and a medium storing the method, more particularly relates tothe method, the system, and the medium which provide calculatingdistances between elements mounted on each surface of a printed circuitboard.

2. Description of the Related Art

A calculation of a distance between elements mounted on each surface ofa printed circuit board (PCB), can make it possible to evaluateinfluences of noise caused by a possible creepage discharge. Thedistance is measured along the surfaces, the distance is referred to asthe creepage distance hereinafter, and the distance should be evaluatedwhether to agree or not with requirements in specifications and/orstandards.

The layout of elements formed or arranged on PCBs is usually designedwith a computer aided design system, hereinafter referred to as CADsystem. In case of use of the CAD system, the creepage distance can becalculated by a function of the CAD system, where the creepage distanceis a distance measured along a surface of a PCB between an elementmounted on a front surface of a PCB, the element is referred as to thefront element hereinafter, and other element mounted on a rear surfaceof the PCB, the other element is referred as to the back element. Andthe resultant creepage distance is judged or evaluated whether it agreesor not with the requirements.

A conventional measurement is explained in detail with referring toFIGS. 19A and 19B, where FIG. 19A is perspective view and FIG. 19B is aside view. A distance LA between a front element 710 and a side 712 of afront surface 702 of a PCB 700, a thickness LC of the PCB 700, adistance LB between a back element 720 and the side 712 are measuredrespectively. And then a creepage distance between the two elements isgained by summing the distances LA and LB and the thickness LC. However,a following consideration on the path to measuring the distance isnecessary in case of particular locations of the elements.

As shown in FIGS. 20A and 20B, a pair of elements 710 and 720, each ofthem being arranged on both surfaces of the PCB 700, normal lines NA andNB can be overlapped as shown in FIG. 20B. In this case of the locationsof elements 710 and 720, the creepage distance can be gained as themethod described above. However, in case of locations of elements 710and 730, there is no common normal line being normal to the side 712. Inthis case, an operator must estimate a point α which gives the minimumsum of the distances DA and DB, where DA is a distance between theelement 710 and the point α and DB is a distance between the element 730and the point α. The selection of the point α is subjectively estimatedand selected by the operator. The creepage distance, in this case, isgiven by the sum of DA, DB and the thickness LC of the PCB 700. Thus onthe CAD system, a function to calculating a distance of two pointsselected by the operator is provided. The operator can gain the creepagedistance by use of the function.

Other method of calculating of the creepage distance is disclosed in aJapanese publication of unexamined application 2005-10835. The method inthe publication is disclosed as a function in an insulation-evaluatingsystem. The system itself comprises a process transforming a threedimensional model to a correspondent approximate polyhedron model, aprocess of topologically recognizing the polyhedoron model, a process ofrecognizing a relation with adjacent parts, a process of recognizing andcreating data of voltage system, a process of extracting a pair ofvoltage systems including a problem by rough check, a process ofcalculating “a creepage distance” between both the voltage systems, aprocess of checking the creepage distance by the information in aspecification for insulation, and a process of outputting theinformation of the voltage systems including problems.

In the prior art shown in FIGS. 19A, 19B, 20A, and 20B, the creepagedistance is obtained as the summation of the thickness of the PCB andthe distances calculated by a computer between a turning point andpoints on the front and back elements, where these three points shouldbe indicated by the operator. Thus till obtaining a result, the methodin the prior art requires frequently operation by the operator, andimposes on the operator the serious burden and requires a long time.Further, the resultant creepage distance is not guaranteed as the pathhaving the minimum distance between both elements, because the turningpoint and the points on the front and back elements are subjectivelyselected by the operator. Therefore, the method in the prior artinvolves a problem that the resultant distance as a creepage distancehas serious error and a low reliability.

Furthermore, it is necessary to obtain all creepage distances for everypossible combinations of a plurality of elements arranged on the bothsurfaces of PCB. Therefore, it will be vast time to calculate the everycreepage distances even if the turning point and the points on the frontand back element are set automatically instead of the operator, becausethe combination of the points for calculating the creepage distances areenormous. Subsequently to detecting front and back element notcompatible with the requirement in the specification or a standard, thesimilar calculation must be repeated after the rearrangement of thefront elements by the operator so that the elements become to becompatible with the requirement. Therefore, the prior art has problemssuch that the method imposes serious burden on the operator and requiresa vast time for a whole design process.

In the method disclosed in the Japanese publication of unexaminedapplication 2005-10835, the calculation of the creepage distancerequires the process of transforming the three dimensional model to acorrespondent approximate polyhedron model and so on. The calculation inthe process of transforming and the like are too vast to obtain thecreepage distances between the front and back element on the PCB. Thedisclosed method in the application is suitable for analyzing a objecthaving a complicate structure. In case of an object having a simplestructure such as a rectangular contour of PCBs, it is desired to obtainin a short time the distances between elements on the PCB by a simplecalculation such as summation of a distance from an element to a side ofthe PCB, the thickness of the PCB, and the distance from the side toother element.

SUMMARY OF THE INVENTION

The present invention is provided to solve the problems described above.The present invention is capable of detecting accurately the elementsbetween which a creepage distance should be calculated, and of improvingthe time for processing the calculation of the distances. Furthermore,the object of the present invention is to provide a computer aideddesign system capable of accurately calculating the creepage distancesin a short time.

According to one aspect of the present invention, there is provided amethod for supporting design of a printed circuit board for mounting aplurality of elements disposed on both the major surfaces of the printedcircuit board, respectively, the method comprising, a step of creating acopy and a mirror copy of plan views of the major surfaces of theprinted circuit board, respectively, a step of performing a calculationfor obtaining a shortest straight line distance between one of theelements appearing in the copy and another of the elements appearing inthe mirror copy when the copy and the mirror copy are placed side byside across a null thickness of the printed circuit board; and a step ofobtaining a creepage distance between the two elements, the creepagedistance being equal to a summation of a value of the thickness and avalue of the shortest straight line distance.

According to another aspect of the present invention, there is providedan apparatus for supporting design of a printed circuit board formounting a plurality of elements disposed on both the major surfaces ofthe printed circuit board, respectively, the apparatus comprising: meansfor creating a copy and a mirror copy of plan views of the majorsurfaces of the printed circuit board respectively, the copy and themirror copy being placed side by side across a null thickness of theprinted circuit board; means for calculating a creepage distance betweenone of the elements appearing in the copy and another of the elementsappearing in the mirror copy, the creepage distance being equivalent toa summation of a distance and a thickness of the printed circuit board,the distance being a shortest straight line distance, the shorteststraight line distance being between the one of the elements appearingin the copy and the another of the elements appearing in the mirrorcopy; and means for extracting the one of the elements appearing in thecopy, the one of the elements appearing being within the creepagedistance from the another of the elements appearing in the mirror copy,the creepage distance being less than a predetermined distance.

According to still another aspect of the present invention, there isprovided, a method for computer-aided design concerning this inventioncomprising a mirror copy procedure around a side of the PCB, where thePCB board has the width component, depth component, and board thicknesscomponent, and the procedure of calculating the shortest distance in astraight line between the back target element to be calculated on theback surface of the PCB and the element which is a mirror-copied, whereit is supposed that there is nothing about the component of thedirection of board thickness. And a calculating procedure for obtainingthe creepage distance by the summation of the shortest distance in astraight line and the thickness of the PCB. Thus, the distance in astraight line between the back target element and the mirror copiedelement is obtained under the condition of the thickness od the PCBequal to zero, and then the creepage distance is obtained by adding thethickness disregarded of the PCB to the distance. Accordingly thecreepage distance can be obtained correctly and quickly by calculating acreepage distance as a distance on a straight line.

According to yet another aspect of the present invention, there isprovided a method for computer-aided design including a mirror copyprocedure around a side of the PCB, where the PCB board has the widthcomponent, depth component, and board thickness component, and theprocedure of calculating the shortest distance in a straight linebetween the back target element to be calculated on the back surface ofthe PCB and the element which is a mirror-copied, where it is supposedthat there is nothing about the component of the direction of boardthickness. And the method includes a procedure in which a creepagedistance is obtained as the summation of the shortest distance in astraight line and the thickness of the PCB. The method further includesa procedure in which elements having a creepage distance within apredetermined distance are extracted. Accordingly, in the presentinvention, since the calculated creepage distance between a frontelement and a back target element is compared with the predetermineddistance and the elements apart within a creepage distance less than thepredetermined distance are extracted, the elements arranged incorrectlyautomatically and quickly can be specified.

According to yet still another aspect of the present invention, there isprovided a method for computer-aided design comprising; a mirror copyprocedure for mirror copying symmetrically a target element about a sideof a board of a PCB to be calculate, the target element being on a frontsurface of the board, where the board has the width component, depthcomponent, and board thickness component; a procedure of detecting aback element on a back surface of the board in a distance from a pointon the mirror copied element, the distance being a distance subtractedthe board thickness from a predetermined allowable distance, supposingthat there is nothing about a board thickness component; a procedure ofcalculating a shortest distance in a straight line of the back elementand the mirror copied element, and of adding the thickness to theshortest distance to obtain a creepage distance, supposing that there isnothing about the board thickness component; and, a procedure ofextracting element within a distance less than the predeterminedallowable distance. Thus, the creepage distance is found by using onlythe back target element which is in the distance subtracted the boardthickness from the predetermined allowable distance from the point onthe mirror copied element, supposing that there is nothing about theboard thickness component. Accordingly, procedure for finding thecreepage distance is performed only for specified elements not for allthe back elements. Therefore, the method can avoid unnecessarycalculation and extract quickly elements in incorrect arrangement.

According to above aspect of the present invention, there is providedthe method comprising; when the element in the creepage distance lessthan the predetermined allowable distance is extracted, an intersectionof the straight line from the mirror copied element to the back targetelement and a side of a board of a PCB is calculated as a turning point,and a procedure of outputting two line segments as a path to means fordisplaying, the two line segments comprising a first line segment fromthe target element to the point and a second line segment for the pointto the back target element as a path; and, a procedure of displaying thepath. Thus, the turning point is obtained by use of the mirror copiedelement, and the path is outputted to means for displaying, the pathcomprising the two line segments from the target element to the pointand the point to the back target element, and the target element and theback target element are also displayed. Accordingly, a user grasps whichelement is incorrect arrangement easily, even can grasp the pathassociated with the incorrect arrangement. When a plurality of paths aredisplayed, the element in severe incorrect arrangement can be graspedespecially as incorrect arrangement.

The present invention also provides a computer-aided design systemcomprising; means for obtaining an element mirror-copied from a firstelement, the first element disposed on one of two surfaces of a printedcircuit board, the element mirror copied and the first element beingsymmetrical about a selected side of the printed circuit board; meansfor calculating a creepage distance between the first element and asecond element disposed on other of the two surfaces, the creepagedistance being equivalent to a summation of a distance and a thicknessof the printed circuit board, the distance being a shortest straightline distance under a condition, the shortest straight line distancebeing between the element mirror-copied and the second element, thecondition being a null thickness of the printed circuit board; and meansfor extracting the second element, the second element being within thecreepage distance from the first element, the creepage distance beingless than a predetermined distance

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a block diagram showing the configuration ofa printed circuit board design support apparatus of the presentinvention;

FIGS. 2A to 2F show data table structures concerning the embodiment ofthe present invention;

FIG. 3 shows a diagram of selection of the front element concerning theembodiment of the present invention;

FIG. 4 shows a diagram of a mirror coping of the front elementconcerning the embodiment of the present invention;

FIG. 5 shows a diagram of selection of the back target elementconcerning the embodiment of this invention;

FIG. 6 shows a diagram of the creepage distance calculation concerningthe embodiment of the present invention;

FIG. 7 shows a diagram of the path of the element group concerning theembodiment of the present invention;

FIG. 8 shows a diagram for deriving the path of the element groupconcerning the embodiment of the present invention;

FIG. 9 shows a flowchart which shows an example of extracting processingof the incorrect arrangement of elements;

FIG. 10 shows a flowchart which shows an example of extractingprocessing of the incorrect arrangement of elements;

FIG. 11 shows a flowchart which shows an example of confirmingprocessing of the incorrect arrangement component after relocationconcerning the embodiment of this invention;

FIG. 12 shows a diagram showing the front element moved by editconcerning the present invention;

FIG. 13 shows a diagram of recalculation of the creepage distance;

FIG. 14 shows a diagram of re-derivation of the path;

FIG. 15 shows an outline diagram of all the processes centering onoperation of the user of the present invention;

FIGS. 16A and 16B show diagrams of an example the circuit networkconcerning of the present invention;

FIG. 17 shows a diagram of calculation of creepage distance in case ahole exists in the board concerning the present invention;

FIG. 18 shows a diagram of another method of calculation of creepagedistance concerning the present invention;

FIGS. 19A and 19B show diagram of calculation of the creeping distancein prior art; and

FIGS. 20A and 20B show diagram of calculation of the creeping distancein prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments are explained with reference to FIGS. Thepresent invention can be realized in various embodiments. Therefore, thepresent invention should not be recognized within the followingembodiments. The explanation is directed to the system, while thepresent invention can be embodied also as a program to be able to beused in a computer or as a method by, so-called, the person skilled inthe art. The present invention can be embodied as hardware, software, orcombination of software and hardware. The program can be stored in ahard disk, a compact disk ROM, a digital video disk ROM, an opticalmagneto storage device, magnetic storage device, and a computer readablemedium. Further, the program can be stored other computer via a network.

A preferred embodiment of the present invention is shown in FIG. 1 as acomputer-aided design system (CAD system) 1. In FIG. 1, essential partsof the CAD system 1 are shown as a block diagram, and the system 1 maybe embodied with a digital computer such as a personal computer or awork station. The CAD system 1 comprises a standard CAD system 100, aninput device 10, a means for selecting a front element 20, a means formirror-copying 30, a means for selecting back element 40, a means forcalculating a distance 50, a means for selecting a pair of elements inincorrect layout 60, a means for displaying the pair in incorrect layout70, an output device 80, a means for detecting a path on elements 91, ameans for detecting element defining the path 92, a means for confirmingelement to be edited 93. The standard CAD system 100 can performfunctions of enlargement, reduction, rotation, and the like which areused in designing a PCB, and the explanation on the standard CAD system100 is abbreviated, because it is well-known, and is properly realizedby various technologies.

The input device 10 reads out data for designing a figure, such as aboard, elements disposed on the PCB, dimensions of the board, from astorage device such as a device for storing temporal data 96, a database97, or the like. And the input device 10 can receive data, such as datafor designing a figure, from the standard CAD 100. And then the inputdevice 10 sends the data to the means for selecting a front element 20,the means for mirror-copying 30, the means for selecting back element40, the means for calculating a distance 50, the means for selecting apair of elements in incorrect layout 60, the means for displaying thepair in incorrect layout 70, the means for detecting a path on elements91, the means for detecting element defining the path 92, the means forconfirming element to be edited 93.

FIG. 2A to FIG. 2F show schematically formats of data stored in adatabase 97 for the CAD system 1 for designing a PCB in the embodiment.FIG. 2A shows the format of common data 310, such as the thickness ofthe PCB 312, the predetermined allowable distance 314, and theattribution 316 of storage location of the data such as the thicknessand the allowable distance. FIG. 2B shows the information of the board320 to be calculated. The format of the information of the board 320includes each attribution of the identification code 322 assigned to ashape of the board of the PCB to be calculated, the identification data324 for identifying contour or hole, and the shape data 326 of theboard. The “contour” in the attribution of the identification data 324shows a side in the external shape, and the hole shows the side of thehole formed within the board. FIG. 2C shows the information regarding afront element to be calculated concerning to a side. The format of theinformation 330 includes each attribution of the identification code orthe code 332 for discrimination, the identification code of themirror-copied element 334, the name of net in circuit 336, and the shapedata of the mirror-copied element 338. The database includes a table forall front elements, the table has each attribution of the identificationdata, the name of net in circuit, and the shape data of front element.

FIG. 2D shows the information for the back elements 340, as objects forcalculating, which are detected on the basis of the shape of themirror-copied element. The information includes each attribution of theidentification code of the back element 342, the name of net 344 in acircuit, and the shape data of the back element 344. The databaseincludes also a table for all back elements, the table has eachattribution of the identification data of the back element, the name ofnet in circuit, and the shape data of back element. In this embodiment,the table for resultant calculation as shown in FIG. 2E includes eachattribution of the identification codes of front elements 352 and backelements 354, the calculated creepage distance 356, and the pathinformation 358. The table 360 shown in FIG. 2F includes the attributionof the initial points 362 and the terminal points 364 and thegeometrical data of the calculated path 366.

The means for selecting the front element 20 has a function whichselects element possibly not to be compatible regarding the creepagedistance with a requirement in a specification or a standard, where theelement has been arranged on the surface as the front one selected fromthe both surfaces of the board. In detail, one side of the board isselected, and then the elements located within an modified allowabledistance normal to the side are detected, where the modified allowabledistance is the allowable distance minus the thickness of the board 312in FIG. 2A. FIG. 3 shows a diagram for explanation of selecting a frontelement based on the embodiment. The area within the modified allowabledistance L′ 420 in normal direction to a side 410 of the board 400 isshown as a rectangle 428 drawn with a dash-single dot line. Among thefront elements 422, 424, 426, the front element 422 is selected as thefront target element by the means for selecting the front element 20,because only the front element 422, hereinafter referred as to the fronttarget or target element 402, is located within the rectangle 428, wherethe front target element 422 is enclosed by an ellipse drawn by adash-single dot line.

The means for mirror-copying 30 has a function creating an image of aturned over element associated with the front element around a side ofthe board as a symmetrical axis for turning over. The image, hereinafterreferred as to the turned over element or the mirror copied element, issymmetrical with the front target element 422 around the side. FIG. 4shows a diagram for explanation of mirror-copying a front target element422 based on the embodiment. The shape design data sent from the inputdevice 10 (FIG. 1) includes the shape data of the board 400 and theelement shape data of front target element 422. By the function of themeans for mirror-copying 30, the element shape data of the turned overelement (mirror copied element 434) is obtained based on the targetelement shape data selected by the means for electing the front element20. In the FIG. 4 the front target element 422 and the mirror copiedelement 434 are apart LM from the side 410 and L′ shows the modifiedallowable distance.

The means for selecting back element 40 has a function which selects theback element, which are arranged on the back surface of the board,possibly not to be compatible regarding the creepage distance with arequirement in a specification or a standard. An area including backtarget element to be detected is obtained, because the means formirror-copying 30 specifies the mirrored target element and the modifiedallowable distance L′ is known. FIGS. 4 and 5 show diagrams forexplanation of selecting a back element based on the embodiment. Thearea 435 to be searched, which is drawn with a dash-single dot line inFIG. 4, is ranging from the mirror copied element 434 to the modifiedallowable distance L′ in directions of west, east, and in directiontoward to the board 400. Further for more accurate area, the area 433drawn with the dash-double dots line can be selected as the area to besearched. The means for selecting back element 40 detects as the backtarget elements back elements 440, 442, and 446, which are cross-hatchedand enclosed with each ellipse drawn with broken line, since they havean intersection with the area 435 as shown in FIG. 5.

The means for calculating a distance 50 has a function which calculatesthe minimum distance from the mirror copied element 434 to the backtarget element. FIG. 6 shows a diagram for explanation of calculating acreepage distance based on the embodiment. Each minimum distance betweenone mirror copied element 434 to three back target elements 440, 442,446 is shown with the arrows respectively. The means for calculating adistance 50 calculates each distance shown by the arrows 436, 436′, 436″and adds the value of the thickness of the board 400 to the each valueof the distance to obtain the respective creepage distance. Each elementsuch as 440, 442, 446, and 446 has in detail a predetermined area. Forexample, in case of the conductive pattern for use of electricalconnection, the area can be defined with two straight lines and twocircular arc of a half circle. The algorithm to obtain the minimumdistance between two area having each region described above is wellknow to design and realize a method to calculate the minimum distancebetween two area by a skilled person in the art. However the presentembodiment uses the method described below, from the view point of ahigh speed processing. And the method is not well known. At first, thearea of one of the elements is transformed into a segment. And theminimum distance between the other area and the segment is calculated byuse of the well known algorithm. Or the area regarding two element aretransformed into each segment, and the minimum distance between the twoelements is calculated by use of the well known algorithm. Furthermoreby use of the well known algorithm, it is possible to obtain the minimumdistance between each end of the segment and the area of the otherelement or the segment obtained by transforming the other area.

The means for selecting a pair of elements in incorrect layout 60 has afunction which compares the allowable distance and the creepage distanceobtained by the means for calculating a distance 50. Comparing the twodistances, the front target element and the back target element isdecided as a pair of elements not compatible with requirement in aspecification or a standard if the creepage distance shorter than theallowable distance.

The means for displaying the pair in incorrect layout 70 has a functionwhich obtains a path between a pair of the target element and backtarget element detected by the means for selecting a pair of elements inincorrect layout 60. FIGS. 7 and 8 show diagrams for explanation ofderiving a path in the embodiment. In detail, the intersection of thepath 436 and the side 410 of the board 400 is obtained as a turningpoint 450, where the path 436 corresponds to the minimum straight linedistance of the mirror copied element 434 and the back target element440. And the point on both the path 436 and the mirror copied element434 is obtained. And next, an intersection of the straight line 451 andthe front target element 422 is obtained, where the straight line 451crosses the point on the mirror copied element 434 and is normal to theside 410. The intersection also can be analyzed by the calculation formirror copying the front element around the side 410 as a symmetricalaxis, because the intersection is corresponding to the point on themirror copied element 434. As a result, the line is obtained as a path452 in FIG. 8, where line crosses the point on the back target element440, the turning point 450, and the point on the front target element422.

The output device 80 outputs the data of the object side, such as theside 410, the front target element, such as 422, the back targetelement, such as 440, and the path, such as the path 452, which areobtained with the means for selecting a front element 20, the means formirror-copying 30, the means for selecting back element 40, the meansfor calculating a distance 50, the means for selecting a pair ofelements in incorrect layout 60, the means for displaying the pair inincorrect layout 70, the means for detecting a path on elements 91, themeans for detecting element defining the path 92, the means forconfirming element to be edited 93. The data is output to the means fordisplaying data, such as the display 98 in FIG. 1, a main memory device(not shown in FIG. 1), other storage device, such as the device forstoring temporal data 96, or a printing device( not shown in FIG. 1).

The means for detecting a path on elements 91 has a function whichsearches figure data of the path to obtain the path passing thecoordinate expressing the element. The means for detecting elementdefining the path 92 has a function which searches figure data to obtainthe element indicated by the path. The means for confirming element tobe edited 93 has a function which decides whether the element relocatedby an operator is an element in incorrect layout or in proper layout.

The front and back surfaces of the board are apart each other at adistance of the thickness of the board. Therefore, each element arrangedon the both surfaces has the different coordinate respectively in thedirection of the thickness of the board. Usually, the reference of thedirection of thickness is given at the back surface of the board, so thecoordinate in the direction of the thickness of the back target elementis zero, and the coordinate of the element on the front surface equalsto the thickness of the board. Therefore, the neglect of the coordinateequivalent to the thickness of the board brings that each elementarranged on the both surfaces of the board is considered on the sameplane, such as the same surface of the board. Then the creepage distancebetween the front element and the back target element can be obtain asthe summation of the distance between the mirror-copied element of thefront element and the back target element and the thickness of theboard. If the coordinate of one of the front or back surfaces is notzero but the front and back surfaces are parallel, it is possible toobtain the creepage distance can be obtain in the same manner describedabove.

FIG. 9 shows an example of a flowchart of a process for selecting a pairof elements in incorrect layout. With referring to FIGS. 1 and 9, theprocess is explained. In the present embodiment, the process starts atStep 200 and begins substantially a process at Step 201. At Step 201,the means for selecting a front element 20 detects a front elementplaced within a region which occupies area within a distance equal tothe allowable distance minus the thickness from the selected side of theboard. When a plurality of the front elements are detected, the eachidentification code corresponding to the each front element is stored asa front target element in the device for temporarily storing data 96 inFIG. 1. And in Step 202, the means for mirror-copying 30 mirror-copiesthe front target element around the selected side as a symmetrical axis,where one of the front target elements is select in the case of theresultant plural front target elements. In Step 203, the means forselecting back element 40 specifies the mirror copied element and aregion to be detected within the modified allowable distance from themirror copied element. In Step 204, the means for selecting back element40 detects as a back target element a back element within the specifiedregion. When a plurality of the back target elements are detected, theeach identification code corresponding to the each back target elementis stored as the back target element in the device for temporarilystoring data 96 in FIG. 1. In Step 205, the means for calculating adistance 50 calculates the shortest straight line distance from themirror copied element to the back target element, where one of the backtarget elements is selected for the calculation if the back targetelements are plural. And in Step 206, the means for calculating adistance 50 sums the thickness of the board and the shortest straightline distance to obtain the creepage distance. In Step 207, the meansfor selecting a pair of elements in incorrect layout 60 compares theobtained creepage distance with the allowable distance and decideswhether the creepage distance is shorter than the allowable distance ornot. In Step 207, the creepage distance is longer than the allowabledistance, the process jumps to Step 211, while the output device 80outputs the pair of the element to the memory in Step 208 in the case ofthe creepage distance being shorter than the allowable distance in Step207 the process. And the process goes to Step 211.

In Step 211, it is judged whether the back target element is last thelast one or not. When it is judged, in Step 211, the back target elementis not the last in the case of the back target element detected in Step204 being plural, other back target element is taken into as the backtarget element in Step 212, and then the process returns to Step 205.These steps can obtain every creepage distance for the all back targetelements detected in Step 204 and can detect any pair in incorrectlayout.

When in Step 211 it is judged that the back target element is the lastone, the process goes to Step 221, where it is judge whether the targetelement processed in the Step 221 is the last one or not. When in Step222 it is judged that the target element is not the last one in the caseof the plural target elements being detected in Step 201, other targetelement is taken into as the target element and the process returns toStep 202. These steps can obtain every creepage distance for the alltarget elements and back target elements detected concerning a side ofthe board, and can detect any pair in incorrect layout.

When in Step 221 it is judged that the target element is the last one,the process goes to Step 231, where it is judged whether the side is thelast one or not. Usually the board has at least four sides, then it isnecessary to check whether there are any pair of the front and backelements in incorrect layout concerning to each of the sides. Therefore,in Step 231, when it is judged that the side is not the last one, otherside is taken into as the side and the process returns to Step 201.

All the pairs of front and back elements in incorrect layout about therelation between the front and back surfaces on the PCB are extracted atthe above Step 232. Next, it searches for one path at a time from thesepair of front and back elements. First, the intersection of the targetside of the board and the shortest straight line from the mirror copiedelement and the back target element, where the shortest straight line isone used to obtain the creepage distance, is obtained as a turning point(Step 241). Next, the means for displaying the pair in incorrect layout70 identifies the point on the target element corresponding to theintersection of the shortest straight line and the intersection on themirror copied element in Step 242. In Step 243, the output device 80outputs the each data of the point on the back target element, theturning point, and the intersection on the target element. In Step 244,it judges whether it is the last pair of elements, if it is the last,the process will end, and if it is not the last, the process will returnto Step 241 for the following pair of elements.

The information on the elements which are derived from the aboveprocess, such as the mirror copied element, the back target element, thecreepage distance the path exists on memory, and the output device 80stores the information in the database. Although the derivation time ofeach information is sufficient as the timing of storing, it is moreefficient to store the information on memory collectively.

The CAD standard means 100 receives the output of the pair of elementsand a path, and specifies and displays on the PCB the front element, thepath, and back element, where the a pair of the front and back elementsis in a incorrect layout. Changing a color and displaying the front andthe back elements which serve as incorrect layout compared with theelements used as correct layout, are displayed for example. Therefore auser can recognize that to display the path shows the pair of theelements in incorrect layout. Although the elements and the path isdisplayed on the display through the CAD standard means 100, the outputdevice 80 can also display directly them on a display to specify them onthe screen. Furthermore, the pair of elements in incorrect layout andthe path concerning not all sides but a side which is specified by theuser can be displayed on the screen to decrease the load to display themon the screen from a view point of processing in the output devices 80.Furthermore, the back target element in incorrect layout and the pathconcerning a target element specified by the user can be displayed, andthe reduction of incidence of a display process also can be performed.When the user actually rearranges the surface element in incorrectlayout, as described later, and just a display in the required range isenough.

FIG. 11 is the flow chart which shows an example of the flow of the pairof elements in incorrect layout confirming processing after relocationin the embodiment of this invention. The user is able to edit anelement, where the said pair of elements in incorrect layout componentgroup and the associated path are displayed on the screen. In responseto the editing operation from the user, the CAD standard means 100performs a display change processing for migration of the element andCAD data changing. With treatment of the CAD standard means 100 inregard to the editing operation to the element, the creepage distancecalculation is performed again, and the process is performed to confirmthat the element remains in incorrect layout or not by a comparison withthe allowable distance. Specifically, it is as follows. That is, thefront element which serves as an editing element by the CAD standardmeans 100 in response to the editing operation starting in Step 250 bythe user for the front element is specified first (Step 251). The meansfor detecting a path on elements 91 detects a path crossing thecoordinate of the specified element (Step 252). ID of the element whichthe detected path indicates is detected from the graphic data of a pathby the means for detecting element defining the path 92 (Step 253). Inresponse to a user's editing operation, the CAD standard means 100performs editing processing of the front element as an editing object(Step 254). For example, a front element 422 moves from the display ofthe state of FIG. 8, and it changes to the moved element 460 of thestate of FIG. 12. ID of the target element moved by the means forconfirming element to be edited 93 is judged whether the ID is inagreement with ID of the target element obtained at Step 253 (Step 255).When there is a plurality of element IDs, the process for the judgmentis repeated.

The process ends when in Step 255 the means for confirming element to beedited 93 judges that the ID is not in agreement with ID of the targetelement obtained at Step 253. In the case of the target element crossingthe path associated with other target element, the ID of the elementobtained in the process of Step 253 may not agree with the ID of targetelement.

When the means for confirming element to be edited 93 judges in Step 255that the ID agrees with ID of the target element obtained, the mirrorcopying means 30 creates the mirror copied element 470 of the frontelement 460 centering on the side 410 (Step 261, and see FIG. 13). Forexample, it becomes as it is shown in FIG. 13 by the mirror copy of thefront element 460 edit. The distance calculation means 50 calculates theshortest straight line distance 472 from the mirror copied element 470to the back target element 440, where one back target element is chosenwhen there are a plurality of back element to be consider (Step 262).The distance calculation means 50 adds board thickness to the foundshortest straight line distance, and finds creepage distance (Step 263).The creepage distance obtained by the means for selecting a pair ofelements in incorrect layout 60 is compared with the allowable distance.In Step 264 it is judged whether the creepage distance is smaller thanthe allowable distance or not. In Step 264, if the means for selecting apair of elements in incorrect layout 60 judges the creepage distance isshorter than the allowable distance, the process goes to a path updateprocess which has been defined (Step 270). However, in Step 264, if themeans for selecting a pair of elements in incorrect layout 60 judges thecreepage distance is longer than or equals the allowable distance, theprocess goes to the path elimination procedure (Step 280) which has beendefined.

In a path update process (Step 270), treatment of said step 241 or Step243 is made, a new path 476 is generated, and an old corresponding pathis deleted. If change is reflected in a display through these treatment,it will become as it is shown in FIG. 14. In a path delete process (Step280), an old corresponding path and a corresponding component group aredeleted. The path on memory and a component group are updated, and alsothe information in a database is updated by the outputting part 80.

After termination of Step 270 or 280, it will be judge whether the backtarget element processed is the last back target element or not (Step291). When it is judged that the back target element is the last one,the process ends and shifts under control of the CAD standard means 100.When it is judged at said step 291 that the back target element is notthe last one, the process returns to Step 261 for the following backtarget element.

The path and the element specified by the path is not read from adatabase at Step 252 and Step 253, but the path and the element arespecified from graphic data, because searching them from graphic datacan process at high speed rather than obtaining through access to adatabase. However, the method realized by access to a database dependingon the environment of the computer system to build may be able toprocess at high speed.

FIG. 15 is an outline diagram of all the processes focusing onoperations of a user. First, the user designs by performing an editingtask, displaying graphic data 500 on the display 98 using the CADstandard means 100 ((1) in FIG. 15). The user directs measurement ofcreepage distance, and judgment of incorrect arrangement to the featuresection of this invention after termination of the design ((2) in FIG.15(2)). Creepage distance is found through the process which the featuresection of this invention described above, the component of incorrectarrangement is extracted, and the path of the component of incorrectarrangement is calculated. And the path of the component of incorrectarrangement is displayed. To the display of the path, the user checks aresultant measuring and judges the need for revision ((3) in FIG. 15).In this task, when it is judged that there is no necessity for revision,the task ends. If there is the necessity for revision, the editing taskof the PCB will be performed ((4) in FIG. 15). Usually, the position ofparts, such as an electro-conductive pattern and an electric component,is changed, or the shape of an electro-conductive pattern is changed.The user directs re-measurement of creepage distance, and re-judgment ofincorrect arrangement to the feature section of this invention aftertermination of design revision ((5) in FIG. 15). Accordingly, creepagedistance is found through the process which the feature section of thisinvention described above, the component of incorrect arrangement isextracted, and the resultant update path of the component of incorrectarrangement is displayed. To the resultant display on the screen, theuser reconfirms a resultant measuring and re-judges the need forrevision ((6) in FIG. 15). The design of the PCB is completed byrepeating the work of (4) to (6) in FIG. 15 if needed.

[On the Target Element] Also in the incorrect arrangement componentconfirming processing after edit, Step 203 and Step 204 can also beperformed, and the creepage distances between the target element and allthe associated back components can be found, and it can also be judgedwhether there is incorrect arrangement or not. In this embodiment, thecreepage distance and the judge for the incorrect or correct arrangementonly for the component indicated already by the path are performed fromthe viewpoint of the response performance of a system.

[Composition Other than the Composition Called if Needed by theAdditional Function of the CAD Standard Means 100]

Although the system configuration that the feature section is called tothe CAD standard means 100 is explained in this embodiment. But it isnot necessary to compose a module division clearly to the CAD standardmeans 100 and a feature section, and the feature section of the presentinvention completely included in the CAD standard means 100 as well asthe another module which constitutes the CAD standard means 100 can berealized.

In the Case of the Surfaces of the PCB Being Not Parallel to the x-zPlane

The system adopts the coordinate (x, y, z), where x componentcorresponds to the width component of the PCB, z-component correspondsto a depth component, and y-component corresponds to a board thickness,the surface of the PCB is parallel to the x-z plane. In this coordinate,the creepage distance can be obtained by neglect of the component of thethickness as described above. In the case of the x-z plane and thesurface of the PCB being not parallel each other, the creepage distancecan be similarly obtained by re-configurating in the xyz space whichuses the width component of the PCB as x component for the componentused for calculating the creepage distance, uses a depth component as zcomponent, and uses a board thickness component as y component. Thecreepage distance calculation also with same otherwise also carrying outparallel projection of the component used for the creepage distancecalculation to the surface or the back of the printed circuit board isapplicable.

[An Element, the Side, a Circuit Network, and Limitation of the Range]

The target element is detected in this embodiment using the side and thedistance which subtracted board thickness from the allowable distance,and the back target element is found by using the distance from themirror copied element, where the distance is one subtracted the boardthickness from the allowable. Furthermore, an element and the side canbe limited. That is, the user specifies the element and the side to bechecked, and the creepage distance can be found corresponding theelement and the side, and it can be judged whether the element is inincorrect arrangement or not. In detail, the user can specify a certainfront element, a certain back element, or a pair of a certain front andback elements, and a certain side. Thus, the user can search quickly theresult by performing the each operation described above only for theelements and the side specified by the user without performingunnecessary operation.

An element and the side can be specified and also the user can alsospecify a circuit network. The circuit network is formed when carryingout the logical design in which each of the contacting portions ofparts, such as an electric element, is connected by wiring or electroconductive pattern. The user can decide a circuit net name. Thepotential within the wiring or the electro conductive pattern betweenthe contacting portions of parts is same. A text file called a net list(there are various formats) may be created and employed. The netcomposition on a circuit is shown in FIG. 16A, where 530, 540, 550 showeach circuit network. In a CAD system for designing a PCB, wiringbetween actual parts is carried out based on the information of logicalconnection between the parts designed by a CAD system for designing acircuit. FIG. 16B shows the net composition on the PCB. Compared withFIG. 16A, physical composition understands easily by FIG. 16B. (b). Inthis FIG. 16B, the electro-conductive patterns 533, 535, 543, 544, 553and the pads 532, 534, 536, 542, 545, 552, 554 are illustrated aselements. Moreover, only the elements within an area, for example arectangle area, specified by the user can be calculated for the creepagedistance, and it can also be judged whether the element is located inincorrect arrangement.

[In the Case of the PCB Having a Hole]

The side constituting the board is not restricted to the border of theoutside of the PCB. As shown in FIG. 17, for example, the side 621 of ahole 630 formed within the PCB 600 is included in the sides to beconsidered. The creepage distance with the back element 620 detected asa back target element will be calculated by performing said each processof this embodiment to the front element 614 arranged near the hole 630.In this case, although the back component 620 and the back component 622are arranged as the back elements near the hole, the back element 620may become a back target element. This is because in the case thedetection area of detecting the back target element is the range of thedistance which is a distance L′ of the allowable distance minus thethickness of the board in the direction of this side shown with an arrowA on the basis of the mirror copied element 616. By setting the areadrawn with a dash-single dot line for detecting in this way, theincorrect calculation of the shortest distance in a straight linebetween a back element 622 and the mirror copied element 616 is notcarried out, therefore incorrect extraction of a pair of the element inincorrect arrangement is not performed. When the allowable distance islarge, the back element 622 may turn into a back target element, but itcan prevent calculating the mistaken creepage distance by comparing thedistance to a target element and a back target element with the distancefrom the front element to be mirrored to a back target element in such acase. Here, when finding the distance of a target element and the backtarget element w, the distance is found by adding the thickness of theboard to the shortest distance in a straight line not including thethickness without using a mirror copying.

[How to Find Another Creepage Distance]

The board thickness is added to the shortest distance in a straight lineof the mirror copied element to the back target element to find thecreepage distance in this embodiment. However, as shown in FIG. 18, whena target element 660 and the back target element 672 do not exist on thesame vertical line of the side of the PCB, it is possible to calculatethe creepage distance as a following way. Neglecting the thickness ofthe board, the turning point α is selected, where the point α dividesthe segment between a segment into the ratio (A:B=a:b) of the distance Afrom the target element 660 to the side 652 of the PCB 650 and thedistance B from the back target element 672 to the side 652 of the PCB650, the segment is a straight line connecting the each end of theprojected line segment 662 of the target element 660 to the side 652 andthe projected line segment 674 of the back target element 672 to theside 652. The distance A1 from the target element 660 to the point α andthe distance A2 from the point α to the back target element 672, wherethe thickness of the board also is neglected. And then the sum of A1,A2, and the thickness equals to the creepage distance. When the targetelement 660 and the back target element 672 on the back surface of thePCB 650 is normally projected on the side 652 and each of the linesegments 662, 674 projected overlaps each other, the creepage distanceis found by the method performed conventionally.

Although said each above embodiment explains the present invention, itis possible for the technical scope of this invention not to be limitedto the range given in an embodiment, but to add various change orimprovement to each embodiment. The embodiment including such change orimprovement is also contained in the technical scope of this invention.This is clear also from claims.

1. A method for supporting design of a printed circuit board formounting a: plurality of elements disposed on both the major surfaces ofthe printed circuit board, respectively, the method comprising: a stepof creating a copy and a mirror copy of plan views of the major surfacesof the printed circuit board, respectively; a step of performing acalculation for obtaining a shortest straight line distance between oneof the elements appearing in the copy and another of the elementsappearing in the mirror copy when the copy and the mirror copy areplaced side by side across a null thickness of the printed circuitboard; and a step of obtaining a creepage distance between the twoelements, the creepage distance being equal to a summation of a value ofthe thickness and a value of the shortest straight line distance.
 2. Themethod according to claim 1, further comprising: a step of extractingthe one of the elements and the another of the elements, the creepagedistance between the one of the elements and the another of the elementsbeing less than a predetermined distance.
 3. A method for supportingdesign of a printed circuit board for mounting a plurality of elementsdisposed on both the first major surface and the second major surface ofthe printed circuit board, respectively, the method comprising: a stepof creating a copy and a mirror copy of plan views of the first and thesecond major surfaces of the printed circuit board, respectively; a stepof detecting one of the elements appearing in the copy, the one of theelement appearing in the copy being within a distance apart from anotherof the element appearing in the mirror copy, the distance beingequivalent to a distance of subtracting a value of a thickness of theprinted circuit board from a predetermined allowable distance when thecopy and the mirror copy are placed side by side across a null thicknessof the printed circuit board, a step of performing a calculation forobtaining a shortest straight line distance between the one of theelements appearing in the copy and the another of the elements appearingin the mirror copy when the copy and the mirror copy are placed side byside across a null thickness of the printed circuit board; a step ofobtaining a creepage distance between the one of the elements appearingin the copy and the another of the elements appearing in the mirrorcopy, the creepage distance being a summation of the shortest straightline distance and the thickness of the printed circuit board; and a stepof detecting the one of the elements appearing in the copy, the one ofthe elements appearing in the copy being apart within a distance fromthe another of the elements appearing in the mirror copy, the distancebeing less than the creepage distance.
 4. The method according to claim2, further comprising: a step of obtaining a point on the side, thepoint being intersection of a straight line and a side at which the copyand the mirror copy contact each other, the straight line being ashortest straight line segment between the one of the elements appearingin the copy and the another of the elements appearing in the mirrorcopy; and a step of displaying a path, the path comprising a first linesegment and a second line segment, the first line segment being a linesegment between the one of the elements appearing in the copy and thepoint, the second line segment being a line segment between the pointand an element in a copy of plan views of the major surfaces of theprinted circuit board, the element corresponding the another of theelements appearing in the mirror copy.
 5. An apparatus for supportingdesign of a printed circuit board for mounting a plurality of elementsdisposed on both the major surfaces of the printed circuit board,respectively, the apparatus comprising: means for creating a copy and amirror copy of plan views of the major surfaces of the printed circuitboard respectively, the copy and the mirror copy being placed side byside across a null thickness of the printed circuit board; means forcalculating a creepage distance between one of the elements appearing inthe copy and another of the elements appearing in the mirror copy, thecreepage distance being equivalent to a summation of a distance and athickness of the printed circuit board, the distance being a shorteststraight line distance, the shortest straight line distance beingbetween the one of the elements appearing in the copy and the another ofthe elements appearing in the mirror copy; and means for extracting theone of the elements appearing in the copy, the one of the elementsappearing being within the creepage distance from the another of theelements appearing in the mirror copy, the creepage distance being lessthan a predetermined distance.
 6. A method for supporting design of aprinted circuit board for mounting a plurality of elements disposed onboth the major surfaces of the printed circuit board, respectively, themethod comprising: a step of creating a copy and a mirror copy of planviews of the major surfaces of the printed circuit board respectively,the copy and the mirror copy being placed side by side across a nullthickness of the printed circuit board; a step of calculating a creepagedistance between one of the elements appearing in the copy and anotherof the elements appearing in the mirror copy, the creepage distancebeing equivalent to a summation of a distance and a thickness of theprinted circuit board, the distance being a shortest straight linedistance, the shortest straight line distance being between the one ofthe elements appearing in the copy and the another of the elementsappearing in the mirror copy; and a step of extracting the one of theelements appearing in the copy, the one of the elements appearing beingwithin the creepage distance from the another of the elements appearingin the mirror copy, the creepage distance being less than apredetermined distance.
 7. A method for supporting design of a printedcircuit board for mounting a plurality of elements disposed on both themajor surfaces of the printed circuit board, respectively, the methodcomprising: a step of creating a first copy and a second copy of planviews of the major surfaces of the printed circuit board, respectively,the first copy and the second copy being placed across a null thicknessof the printed circuit board; a step of obtaining a first line segmenton a first side corresponding a side of the printed circuit board, thefirst line segment being projected normal onto the first side from afirst element, the first element being one of the elements appearing inthe first copy; a step of obtaining a second line segment on the side,the second line segment being projected normal onto the first side froma second element, the second element being one of the elements appearingin the second copy; a step of obtaining a third line segment, the thirdline segment being a line having two ends, one of the two ends being aend of the first line segment, another of the two ends being a end ofthe second line segment, the end of the first line segment and the endof the second line segment being adjacent each other; a step of dividingthe third line segment into a ratio of a distance from the first elementto the first side and a distance from the second element to the firstside; a step of obtaining a point on the third line segment, the pointdividing the third line segment by the ratio; a step of calculating twodistances, one of the two distances being from the first element to thepoint, other of the two distances being from the point to the secondelement; and a step of obtaining a creepage distance between the firstand the second elements, the creepage distance being a sum of the twodistances and the thickness.
 8. The method according to claim 1, themethod further comprising; a step of detecting the another of theelements appearing in the mirror copy within an area, the area being aregion from a side to a distance, the side being at which the copy andthe mirror copy contact each other, the distance being the predetermineddistance minus the thickness of the printed circuit board.
 9. The methodaccording to claim 1, further comprising; a step of specifying the oneof the elements appearing in the copy and/or the another of the elementsappearing in the mirror copy.
 10. The method according to claim 1,further comprising; a step of specifying a circuit network, the circuitnetwork including the one of the elements appearing in the copy and/orthe another of the elements appearing in the mirror copy.
 11. A methodaccording to claim 4, further comprising: a step of re-arranging anelement appearing in the copy or appearing in the mirror copy; a step ofdetermining whether the element is relating to the path or not; andwherein a calculation is performed again for obtaining the creepagedistance between the two element if the element is one of the twoelement, and a calculation for obtaining a path is performed anddisplayed again if the creepage distance is also less than thepredetermined distance.
 12. A recoding medium readable by a computer andstoring a program which enable the computer to perform a process forsupporting design of a printed circuit board for mounting a plurality ofelements disposed on both the major surfaces of the printed circuitboard, respectively, the recoding medium comprising: a step of creatinga copy and a mirror copy of plan views of the major surfaces of theprinted circuit board, respectively; a step of performing a calculationfor obtaining a shortest straight line distance between one of theelements appearing in the copy and another of the elements appearing inthe mirror copy when the copy and the mirror copy are placed side byside across a null thickness of the printed circuit board; and a step ofobtaining a creepage distance between the two elements, the creepagedistance being equal to a summation of a value of the thickness and avalue of the shortest straight line distance.
 13. A recoding mediumreadable by a computer and storing a program which enable the computerto perform a process for supporting design of a printed circuit boardfor mounting a plurality of elements disposed on both the major surfacesof the printed circuit board, respectively, the recoding mediumcomprising: a step of creating a copy and a mirror copy of plan views ofthe first and the second major surfaces of the printed circuit board,respectively; a step of detecting one of the elements appearing in thecopy, the one of the element appearing in the copy being within adistance apart from another of the element appearing in the mirror copy,the distance being equivalent to a distance of subtracting a value of athickness of the printed circuit board from a predetermined allowabledistance when the copy and the mirror copy are placed side by sideacross a null thickness of the printed circuit board, a step ofperforming a calculation for obtaining a shortest straight line distancebetween the one of the elements appearing in the copy and the another ofthe elements appearing in the mirror copy when the copy and the mirrorcopy are placed side by side across a null thickness of the printedcircuit board; a step of obtaining a creepage distance between the oneof the elements appearing in the copy and the another of the elementsappearing in the mirror copy, the creepage distance being a summation ofthe shortest straight line distance and the thickness of the printedcircuit board; and a step of detecting the one of the elements appearingin the copy, the one of the elements appearing in the copy being apartwithin a distance from the another of the elements appearing in themirror copy, the distance being less than the creepage distance.